PhotoSensor distance

[benjaminDVBD]

We team 3316 are trying to follow the grey lines during the autonomous period.

We want to do this by placing 3 photo sensors, with the middle one following the grey line.
The other 2 photo sensors will be placed on either side of the first one, thus if the robot moves from the line, either one of the two will tell in what direction the robot has turned. In this way the robot can know in what direction to turn in order to continue following the line (and being once more above it with the middle photo sensor).

The problem is that we don't know what the optimal distance between the sensors is.
This is relevant because if it's to close even a small deviation will be "corrected" and the robot will zigzag, and if too far, the robot might not arrive at the peg wall the way we want to.

Any suggestions/ideas?